The subject matter disclosed herein relates generally to the field of permanent magnet synchronous machines and more specifically to a system and method for controlling torque ripples in permanent magnet synchronous machines.
Wind turbine generators are regarded as environmentally friendly and relatively inexpensive alternative sources of energy that utilize wind energy to produce electrical power. A wind turbine generator generally includes a wind rotor having turbine blades that transform wind energy into rotational motion of a drive shaft, which in turn is utilized to drive a rotor of an electrical generator to produce electrical power. Modern wind power generation systems typically take the form of a wind-farm having multiple such wind turbine generators that are operable to supply power to a transmission system that in turn provides the power to a utility system.
These wind turbine generators and wind-farms are typically designed to deliver power to the utility system with the power being independent of system frequency. Some wind turbine generators have a variable frequency operation and require a variable frequency power electronic converter to interface the wind turbine generator output with the utility grid. In one common approach, the wind turbine generator output is directly fed to a power electronic converter where the generator output frequency is rectified and inverted into a fixed frequency as needed by the utility system.
One of the challenges associated with such systems is the amount of acoustic noise produced by the generator. Further, the effect of wind turbine airgap torque ripple on acoustic noise has been largely overlooked. Torque ripple limits are based on managing the noise behavior of the turbine system and avoiding detrimental effects of drive train components. One approach is to design the generator appropriately to reduce the acoustic noise but that has limitations related to increased generator size and cost. It is a challenge to design a cost-effective generator with very low acoustic noise level. Acoustic noise control and therefore the torque ripple control is even a greater challenge for high power applications due to low switching frequency of devices in such applications.